1. Field of the Disclosure
Embodiments disclosed herein relate generally to a process to manufacture liquid epoxy resins by reaction of a polyhydric phenol with an epihalohydrin using an anionic catalyst. The resulting reaction product may then be dehydrohalogenated using an alkali metal hydroxide or alkali earth hydroxide in two reaction steps. The dehydrohalogenation reactions are performed to achieve a high raw material yield while avoiding problems associated with insoluble polymer formation.
2. Background
In the manufacture of epoxy resins, a high raw material yield can be achieved by removing water during dehydrohalogenation with alkali hydroxides to maintain a low water content. However, reactions done under these conditions are susceptible to the formation of insoluble polymers, which can cause problems in the subsequent processing steps.
In contrast, dehydrohalogenation reactions done without water removal can be less susceptible to polymer formation, but also results in a lower raw material yield. Another difficulty with dehydrohalogenation reactions done with water removal is the difficulty in obtaining a product with low variability, because of the sensitivity of product hydrolysable chlorides to the amount of caustic added.
As a result of the above, post-treatment reactions are frequently used to achieve the desired levels of hydrolysable chlorides, and reprocessing of material must often be done.
GB 1278737 discloses a process in which bisphenol-A and epichlorohydrin are reacted with a catalyst, and then dehydrochlorinated using 80-99 percent of the stoichiometric caustic requirement in an azeotropically distilled reactor. Then, the unreacted epichlorohydrin is removed by evaporation and the stripped epoxy resin is combined with a solvent, and then subjected to a second dehydrochlorination reaction.
U.S. Pat. No. 3,221,032 discloses a process in which bisphenol-A and epichlorohydrin are reacted with a catalyst at 125° C. or above, then subjecting the mixture to a dehydrohalogenation reaction using an alkali hydroxide, alkaline earth hydroxide or other base.
U.S. Pat. No. 4,582,892 discloses a process in which bisphenol-A and epichlorohydrin are reacted with a catalyst to form a halohydrin intermediate, then removing the epichlorohydrin and adding a solvent, then subjecting the resulting mixture to a dehydrohalogenation reaction.
CH 575405 discloses a process in which bisphenol-A and epichlorohydrin are reacted with a catalyst to form a halohydrin intermediate, then dehydrohalogenating with an alkali with the excess epichlorohydrin either present or removed. The dehydrohalogenation step is to be done in such a way that no solid salt forms.
U.S. Pat. No. 4,373,073 discloses a process in which bisphenol-A and epichlorohydrin are reacted to form a chlorohydrin ether intermediate, and then a quaternary ammonium catalyst or a similar catalyst is added to accelerate phase transfer reactions during the dehydrohalogenation step.
JP 11158248 discloses a process in which a monofunctional or polyhydric phenol and epichlorohydrin are reacted with 0.2 to 0.9 equivalents alkali metal hydroxide with azeotropic distillation to remove water, and then with additional alkali metal hydroxide after “the pressure is returned to normal” and an organic solvent is added.
JP 58-24578 discloses a process in which a phenol and an epihalohydrin are reacted using a quaternary amine catalyst, then dehydrohalogenated with an alkali hydroxide while removing water.
GB 778887 discloses a process in which a polyhydric phenol and an epihalohydrin are etherified and partially dehydrohalogenated in an alkaline medium using 90-98 percent of an equivalent of alkali metal hydroxide per phenolic hydroxyl equivalent. The excess epihalohydrin is then removed and a second dehydrohalogenation step is performed, optionally in solvent.
Accordingly, there exists a need for processes for the manufacture of liquid epoxy resins (LER) with a high raw material yield and without polymer formation. Such processes should have a high reliability and a low cost. Additionally the processes should have a low variability, avoiding the need to rework product.